Development and transportation of oil and gas fields in increasingly difficult areas pose significant challenges. This includes a significant portion of the subsea fields under development today. One of the most challenging issues is wax deposition inside the transportation and production tubing. This issue is regarded as one of the main flow assurance subjects in subsea and cold climate production where the produced fluids are cooled to below the wax appearance temperature for the fluids [1]. The wax appearance temperature is a property of the oil and can be as high as 65° C. In recent years there has been a significant research effort on the understanding of the deposition and the mitigation of waxing [1-4]. The composition and properties of the wax itself has been quite well understood but a remaining challenge is the monitoring of the wax initiation and growth in the production tubing and equipment. The use of pigs and pressure loss is typically used to monitor pipelines [2, 5]. The problem with pigging inspections is the significant amount of work required to run a pigging operation which might interrupt or possible stop the production temporarily. Pressure loss measurements are typically not sensitive enough to pick up deposition until the deposition has formed a significantly thick layer on the walls of the pipeline.
It would evidently be of considerable value to provide a method by which waxing initiation and/or the extent of waxing can be determined and/or monitored before waxing has reached the severity required to cause a measurable drop in pressure or flow. In particular, if waxing initiation can be detected before a significant layer has built up on the transport system, such as the pipeline or valves, chokes etc thereof then mitigation measures may be used prior to waxing becoming a significant problem. Equally, where waxing might be an issue then mitigation measures can be avoided unless or until initiation of waxing takes place. In such situations the cost and complexity of mitigation measures can be avoided or postponed.
The present inventors have now established that by use of selected labelled waxes or wax-like molecules, a method can be provided to significantly improve the sensitivity and ease by which the onset and growth of wax can be monitored. The authors thus herein disclose a novel method for wax tracing.
In addition to the abovementioned novel wax tracing method, the same monitoring technique can be used for monitoring of precipitation of asphaltenes.